Perform those tasks necessary to synthesize potential prostaglandin antagonists in sufficient quantity and purity to permit adequate testing for antagonist activity. Screen potential prostaglandin antagonists for antagonist activity in the cardiovascular system. Define the antagonist activity as to whether prostaglandins, prostaglandin receptors, or prostaglandin-producing enzymes are being blocked. Determine the degree of specificity of the effective antagonists. Determine the degree of toxicity of the effective antagonists in at least one animal model. Determine the degree of chemical stability of the effective antagonists. Participate in the collaborative efforts of the Coordinating Group.